The present invention generally relates to a micromechanical relay. More specifically, the present invention relates to such a relay having a hybrid drive including both piezo and electrostatic drive elements.
A micromechanical relay having an electrostatic drive is known, for example, from an article by Minoru Sakata: "An Electrostatic Microactuator for Electro-Mechanical Relay", IEEE Micro Electro Mechanical Systems, February 1989, pages 149 to 151. There, an armature which is etched free from a silicon substrate is mounted via two torsion webs on a center line such that each of its two vanes is opposite a base electrode located underneath. Voltage is in each case applied between the armature electrode and one of the two base electrodes for electrostatic excitation of this relay, so that the armature selectively carries out a pivoting movement to one side or the other. A specific wedge-shaped air gap remains between the electrodes even after the pivoting movement, as a result of the separation distance of the torsion mounting, so that the electrostatic attraction force remains relatively low. This also results in a relatively low contact force.
German patent document DE 32 07 920 C2 and related U.S. Pat. No. 4,480,162 relate to an electrostatic relay. There, an armature is etched out of a frame plate made of crystalline semiconductor material. The armature, with the frame plate, is placed onto an insulating substrate which is also fitted with the mating electrode. However, there is a relatively large separation distance between the armature and the mating electrode, which also remains when the armature is attracted. In order to produce the desired contact forces with this separation distance between the armature and the mating electrode, relatively large voltages are required in the case of this known relay.
A relay is described in German patent document DE-C-42 05 029. There, the armature electrode of the tongue-shaped armature forms a wedge-shaped air gap with a base electrode which is arranged inclined with respect to it, on which air gap the armature rolls during the attraction movement until it rests over a large area on the base electrode in the attracted state. This results in a large electrostatic attraction force which ensures an adequate contact force even in the case of micromechanical dimensions.
In addition, it has already been proposed in the document SU-A-738 009 for an electrostatic drive to be combined with a piezoelectric drive in order to achieve a reduced response voltage. However, a diaphragm is proposed there which is clamped in on opposite edges, is composed of a polymeric polyvinylidene fluoride which is intended to act as an armature and is provided with electrodes in order to produce an electrostatic drive. Since, because it is clamped in on two sides, this piezo-film can become effective only by central bending out as a result of a length change produced piezoelectrically, it is not possible to achieve any large electrode surfaces lying on one another in the final state, so that the electrostatic attraction force for producing the contact force must be relatively low.
In general, an electrostatic drive for relays has the disadvantage that the attraction force is relatively low at the start of the armature movement when there is a large separation distance between the electrode, so that the relay responds only with a delay or requires high response voltages. Therefore, an object of the present invention is therefore to develop a micromechanical relay of the type mentioned initially such that the response characteristic is improved, such that the advantages of the electrostatic drive--a relatively high contact force when the armature is attracted--are retained, but the forces at the start of the response are at the same time increased.